Nice start to this build.
Can I suggest hard drive suspension or a custom enclosure for those hard drives? I find that the hard drive noise is the loudest and usually the hardest to silence. Even my WD10EADS with AAM isn't quiet enough for me haha.

Oh and if you're up for some warranty voiding, switch out your power supply fan for a Scythe S-Flex 1600rpm one, it should work quite well in it and remove any remaining noise.